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Chapter 97. Restlet

Restlet Component

The Restlet component provides Restlet based endpoints for consuming and producing RESTful resources.

URI format

Format of restletUrl:
Restlet promotes decoupling of protocol and application concerns. The reference implementation of Restlet Engine supports a number of protocols. However, we have tested the HTTP protocol only. The default port is port 80. We do not automatically switch default port based on the protocol yet.
You can append query options to the URI in the following format, ?option=value&option=value&...


Name Default Value Description
headerFilterStrategy=#refName An instance of RestletHeaderFilterStrategy Use the # notation (headerFilterStrategy=#refName) to reference a header filter strategy in the Camel Registry. The strategy will be plugged into the restlet binding if it is HeaderFilterStrategyAware.
restletBinding=# refName An instance of DefaultRestletBinding The bean ID of a RestletBinding object in the Camel Registry.
restletMethod GET On a producer endpoint, specifies the request method to use. On a consumer endpoint, specifies that the endpoint consumes only restletMethod requests. The string value is converted to by the Method.valueOf(String) method.
restletMethods None Consumer only Specify one or more methods separated by commas (e.g. restletMethods=post,put) to be serviced by a restlet consumer endpoint. If both restletMethod and restletMethods options are specified, the restletMethod setting is ignored.
restletRealm null Use the # notation (restletRealm=#refName) to specify the bean ID of the Realm Map in the Camel registry.
restletUriPatterns=#refName None Consumer only Specify one ore more URI templates to be serviced by a restlet consumer endpoint, using the # notation to reference a List<String> in the Camel Registry. If a URI pattern has been defined in the endpoint URI, both the URI pattern defined in the endpoint and the restletUriPatterns option will be honored.
throwExceptionOnFailure (2.6 or later) true Producer only Throws exception on a producer failure.

Component Options

The Restlet component can be configured with the following options. Notice these are component options and cannot be configured on the endpoint, see further below for an example.
Name Default Value Description
controllerDaemon true Camel 2.10: Indicates if the controller thread should be a daemon (not blocking JVM exit).
controllerSleepTimeMs 100 Camel 2.10: Time for the controller thread to sleep between each control.
inboundBufferSize 8192 Camel 2.10: The size of the buffer when reading messages.
minThreads 1 Camel 2.10: Minimum threads waiting to service requests.
maxThreads 10 Camel 2.10: Maximum threads that will service requests.
maxConnectionsPerHost -1 Camel 2.10: Maximum number of concurrent connections per host (IP address).
maxTotalConnections -1 Camel 2.10: Maximum number of concurrent connections in total.
outboundBufferSize 8192 Camel 2.10: The size of the buffer when writing messages.
persistingConnections true Camel 2.10: Indicates if connections should be kept alive after a call.
pipeliningConnections false Camel 2.10: Indicates if pipelining connections are supported.
threadMaxIdleTimeMs 60000 Camel 2.10: Time for an idle thread to wait for an operation before being collected.
useForwardedForHeader false Camel 2.10: Lookup the "X-Forwarded-For" header supported by popular proxies and caches and uses it to populate the Request.getClientAddresses() method result. This information is only safe for intermediary components within your local network. Other addresses could easily be changed by setting a fake header and should not be trusted for serious security checks.
reuseAddress true Camel 2.10.5/2.11.1: Enable/disable the SO_REUSEADDR socket option. See property for additional details.

Message Headers

Name Type Description
CamelContentType String Specifies the content type, which can be set on the OUT message by the application/processor. The value is the content-type of the response message. If this header is not set, the content-type is based on the object type of the OUT message body. In Camel 2.3 onward, if the Content-Type header is specified in the Camel IN message, the value of the header determine the content type for the Restlet request message. nbsp; Otherwise, it is defaulted to "application/x-www-form-urlencoded'. Prior to release 2.3, it is not possible to change the request content type default.
CamelAcceptContentType String Since Camel 2.9.3, 2.10.0: The HTTP Accept request header.
CamelHttpMethod String The HTTP request method. This is set in the IN message header.
CamelHttpQuery String The query string of the request URI. It is set on the IN message by DefaultRestletBinding when the restlet component receives a request.
CamelHttpResponseCode String or Integer The response code can be set on the OUT message by the application/processor. The value is the response code of the response message. If this header is not set, the response code is set by the restlet runtime engine.
CamelHttpUri String The HTTP request URI. This is set in the IN message header.
CamelRestletLogin String Login name for basic authentication. It is set on the IN message by the application and gets filtered before the restlet request header by Apache Camel.
CamelRestletPassword String Password name for basic authentication. It is set on the IN message by the application and gets filtered before the restlet request header by Apache Camel.
CamelRestletRequest Request Camel 2.8: The org.restlet.Request object which holds all request details.
CamelRestletResponse Response Camel 2.8: The org.restlet.Response object. You can use this to create responses using the API from Restlet. See examples below.
org.restlet.* Attributes of a Restlet message that get propagated to Apache Camel IN headers.
cache-control String or List<CacheDirective> Camel 2.11: User can set the cache-control with the String value or the List of CacheDirective of Restlet from the camel message header.

Message Body

Apache Camel will store the restlet response from the external server on the OUT body. All headers from the IN message will be copied to the OUT message, so that headers are preserved during routing.

Restlet Endpoint with Authentication

The following route starts a restlet consumer endpoint that listens for POST requests on http://localhost:8080 . The processor creates a response that echoes the request body and the value of the id header.
from("restlet:http://localhost:9080/securedOrders?restletMethod=post&restletRealm=#realm").process(new Processor() {
    public void process(Exchange exchange) throws Exception {
                "received [" + exchange.getIn().getBody()
                + "] as an order id = "
                + exchange.getIn().getHeader("id"));
The restletRealm setting in the URI query is used to look up a Realm Map in the registry. If this option is specified, the restlet consumer uses the information to authenticate user logins. Only authenticated requests can access the resources. In this sample, we create a Spring application context that serves as a registry. The bean ID of the Realm Map should match the restletRealmRef.
<util:map id="realm">
	<entry key="admin" value="foo" />
	<entry key="bar" value="foo" />
The following sample starts a direct endpoint that sends requests to the server on http://localhost:8080 (that is, our restlet consumer endpoint).
// Note: restletMethod and restletRealmRef are stripped 
// from the query before a request is sent as they are 
// only processed by Camel.
That is all we need. We are ready to send a request and try out the restlet component:
final String id = "89531";

Map<String, Object> headers = new HashMap<String, Object>();
headers.put(RestletConstants.RESTLET_LOGIN, "admin");
headers.put(RestletConstants.RESTLET_PASSWORD, "foo");
headers.put("id", id);

String response = (String) template.requestBodyAndHeaders("direct:start-auth", 
        "<order foo='1'/>", headers);
The sample client sends a request to the direct:start-auth endpoint with the following headers:
  • CamelRestletLogin (used internally by Apache Camel)
  • CamelRestletPassword (used internally by Apache Camel)
  • id (application header)
org.apache.camel.restlet.auth.login and org.apache.camel.restlet.auth.password will not be propagated as Restlet header.
The sample client gets a response like the following:
received [<order foo='1'/>] as an order id = 89531

Single restlet endpoint to service multiple methods and URI templates (2.0 or later)

It is possible to create a single route to service multiple HTTP methods using the restletMethods option. This snippet also shows how to retrieve the request method from the header:
    .process(new Processor() {
        public void process(Exchange exchange) throws Exception {
            // echo the method

In addition to servicing multiple methods, the next snippet shows how to create an endpoint that supports multiple URI templates using the restletUriPatterns option. The request URI is available in the header of the IN message as well. If a URI pattern has been defined in the endpoint URI (which is not the case in this sample), both the URI pattern defined in the endpoint and the restletUriPatterns option will be honored.
    .process(new Processor() {
        public void process(Exchange exchange) throws Exception {
            // echo the method
            String uri = exchange.getIn().getHeader(Exchange.HTTP_URI, String.class);
            String out = exchange.getIn().getHeader(Exchange.HTTP_METHOD, String.class);
            if ("http://localhost:9080/users/homer".equals(uri)) {
                exchange.getOut().setBody(out + " " + exchange.getIn().getHeader("username", String.class));
            } else if ("http://localhost:9080/atom/collection/foo/component/bar".equals(uri)) {
                exchange.getOut().setBody(out + " " + exchange.getIn().getHeader("id", String.class)
                                          + " " + exchange.getIn().getHeader("cid", String.class));


The restletUriPatterns=#uriTemplates option references the List<String> bean defined in the Spring XML configuration.
<util:list id="uriTemplates">

Using Restlet API to populate response

Available as of Camel 2.8
You may want to use the org.restlet.Response API to populate the response. This gives you full access to the Restlet API and fine grained control of the response. See the route snippet below where we generate the response from an inlined Camel Processor:
from("restlet:http://localhost:" + portNum + "/users/{id}/like/{beer}")
     .process(new Processor() {
         public void process(Exchange exchange) throws Exception {
             // the Restlet request should be available if neeeded
             Request request = exchange.getIn().getHeader(RestletConstants.RESTLET_REQUEST, Request.class);
             assertNotNull("Restlet Request", request);
             // use Restlet API to create the response
             Response response = exchange.getIn().getHeader(RestletConstants.RESTLET_RESPONSE, Response.class);
             assertNotNull("Restlet Response", response);
             response.setEntity("<response>Beer is Good</response>", MediaType.TEXT_XML);

Configuring max threads on component

To configure the max threads options you must do this on the component, such as:
<bean id="restlet" class="org.apache.camel.component.RestletComponent">
  <property name="maxThreads" value="100"/>

Using the Restlet servlet within a webapp

Available as of Camel 2.8 There are three possible ways to configure a Restlet application within a servlet container and using the subclassed SpringServerServlet enables configuration within Camel by injecting the Restlet Component.
Use of the Restlet servlet within a servlet container enables routes to be configured with relative paths in URIs (removing the restrictions of hard-coded absolute URIs) and for the hosting servlet container to handle incoming requests (rather than have to spawn a separate server process on a new port).
To configure, add the following to your camel-context.xml;
   <route id="RS_RestletDemo">
     <from uri="restlet:/demo/{id}" />
       <simple>Request type : ${header.CamelHttpMethod} and ID : ${}</simple>
 <bean id="RestletComponent" class="org.restlet.Component" />
 <bean id="RestletComponentService" class="org.apache.camel.component.restlet.RestletComponent">
   <constructor-arg index="0">
     <ref bean="RestletComponent" />
And add this to your web.xml;
 <!-- Restlet Servlet -->
You will then be able to access the deployed route at http://localhost:8080/mywebapp/rs/demo/1234 where;
localhost:8080 is the server and port of your servlet container mywebapp is the name of your deployed webapp Your browser will then show the following content;
"Request type : GET and ID : 1234"
You will need to add dependency on the Spring extension to restlet which you can do in your Maven pom.xml file:
And you would need to add dependency on the restlet maven repository as well:
    <name>Public online Restlet repository</name>